Electrically operated thermal relay



March 24, 1936. Q, s FIELD ELECTRICALLY OPERATED THERMAL RELAY 2 Sheets-Sheet 1,

Filed Sept. 20, 1952 INVENTOR 055'" 4 BY v /Z ATl'o Em March 24, 1936. o. s; FIELD ELECTRICALLY OPERATED THERMAL RELAY Filed se t'. 20, 1932 2 Sheets-Sheet 2 FIG.4.

Patented Mar. 24, 1936 UNITED STATES PATENT OFFICE ELECTRICALLY OPERATED THERMAL RELAY Application September 20, 1932, Serial No. 634,019

9 Claims.

This invention relates to relays and more particularly to improvements in electrically operated thermal relays.

t In the conventional thermal relay, it is extremely diflicult to maintain a set operating time un-' less the energizing voltage is absolutely constant because any fluctuation in this voltage causes a corresponding change in the current drawn by the heating element. It has also been found difiicult l to maintain a set operating time when the operating elements of such relays are exposed to extremely wide variations in atmospheric temperatures.

In view of the above and other considerations,

i it is proposed in accordance with the present invention to provide a very eificient thermal relay having a current regulated heating unit which is immune to voltage fluctuations and having high contact capacity with absolute compensation for l atmospheric temperature variations, and it is further proposed to manufacture such a relay in a relatively cheap unit which is easily replaceable in case of failure.

Other objects, purposes and characteristic feai tures of the present invention will appear as the description thereof progresses, during which, references willbe made to the accompanying drawings which show the invention in a manner to make it easily understood, rather than with a view to showing the particular construction preferably employed in practice, and in which Fig. 1 is an enlarged elevational view of a relay unit constructed in accordance with the present invention;

% Fig. 2 is a sectional elevational view taken on line 2 2 of Fig. 1 viewed in the direction man,

cated by the arrows;

Fig. 3 is a top sectional view taken on line 3-3 of Fig. 2 also viewed in the direction indicated by the arrows, and

Fig. 4 is a perspective view of a modified form of a relay also constructed in accordance with the present invention.

Referring to the accompanying drawings, a glass bulb l is mounted in a cup-shaped insulating socket 2 by any usual form of basing cement 3. This bulb I, containing the relay elements, which are later described, is either evacuated or filled with an inert gas, such as nitrogen, at a relatively low pressure in the conventional manner through the sealed tip 4, or in other cases, it may be evacuated or gas filled by a tube'(not shown) in the base of the bulb 1, which process is also well known in the art.

Considering first the form shown in Figs. 1, 2,

and 3, a glass supporting stem 5 which is an integral part of the bulb l extends centrally into the bulb and holds an anchor 6 molded therein to the extending end of which is welded one end of a bi-metallic strip 1, which strip 1 extends upwardly 5 with a low resistance contact 8 mounted on its free end. This contact 8 may be a strip of contact metal, such as silver, bent over the free end of the bi-metallic strip 1 as shown and soldered or welded thereto. A longer anchor 9 is moulded into 10 the stem 5 at the right of the anchor 6 and extends upwardly parallel with the bi-metallic strip 1 to which anchor 9 is welded a rectangular piece of metal H) which faces the strip 1 and may be curved as shown in Fig. 3. An anchor ll similar to the anchor 9 is provided at the left of the center anchor 6 and also carries a curved rectangular metallic piece l2 arranged to face the strip 1 in a similar manner to the metallic piece It).

The bi-metallic strip 1 is of any well known construction such as a strip of metal having a high coeilicient of expansion, such as brass, welded to a strip of metal having a low coefficient of expansion, such as Invar. A helical filament I3 is mounted on the side of the bi-metallic strip 1 which has the greater coefiicient of expansion (in this case the right hand side) between the bimetallic strip 1 and the reflector ID. A top support for the filament I3 is provided by a short wire l4 welded to the top of the anchor 9 and a lower support is provided by a wire I5 welded to the lower end of the anchor H, which wire I5 is bent out or U-shaped so as to free the bi-metallic strip 1, and these supports l4 and I5 serve to conduct the electrical energy to the filament l3 through the anchors 9 and II.

Another anchor I6 is molded in the stem 5 at the extreme right hand side to which is welded a bi-metallic L-shaped strip l1 forming a normally made contact'for the lei-metallic strip '1. This 40 contact I! has a low resistance contact point l8 arranged in a similar manner and normally engaging the low resistance point 8 of the strip I. An anchor l9 similar to the anchor i5 is molded into the extreme left hand side of the glass stem 5 to which is welded a bi-metallic strip 20 similarly shaped to the bi-metallic strip I1 and forming the normally open contact for the bi-metallic strip 7, which strip 2!! also carries a low resistance contact point 2| arranged in the same manner as the point l8 of strip l'l.

The anchors 6, 9, H, I6, and I9 which are molded into the glass stem 5 carry smaller leadtend through the glass stem 5 and are brought down to terminal prongs 24 mounted on the bottom of the base 2. These terminal prongs 24 may be molded into the base 2, and being tubular as shown, the wires 23 extend through the hollow center and are soldered to the lower ends thereof. These terminal prongs 24 are standardly arranged on the base 2 such as in the manner adopted for five prong tubes used in radio practice, or in other words, the base 2 is to be mounted in a socket (not shown) thus necessitating that these prongs 24 be so spaced and arranged that the base 2 can be placed in the socket only in one particular position.

The rectangular metallic pieces l and I2 are for the purpose of reflecting the heat and light rays produced by the filament l3 when energized so that these rays are concentrated upon the movable bi-metallic strip 1, and it is desired to be understood that these reflecting pieces may be made straight as well as the curved shape shown herein according to which form is found to be the most practical it being obvious that where maximum efiiciency is desired the curved reflectors will be used. The filament I3 is to be of a material which automatically regulates its energizing current, or in other words a material for this filament is to be chosen which has the characteristic of increasing its resistance as its temperature increases, and it has been found in practice that iron wire is one suitable material for this purpose.

In the particular embodiment shown in the drawings it may be considered that bi-metallic strip 1 is arranged with the metal of the higher coefficient of expansion on the right or filament side thereof and likewise that both contact strips l1 and 20 are arranged with the metal having higher coefficient of expansion on the same side or in this case the right hand side. Thus, it may be seen that, if the strips 1, l1, and 20 are all of a uniform thickness and width, the space between the contact points l8, 8, and 2| will be constant regardless of the temperature to which these parts are exposed because a change in temperature whichwill actuate one of these strips will actuate all three a corresponding amount and in the same direction.

In a thermal-responsive device which is enclosed within an evacuated or gas filled bulb, it

"has been found that the dissipation of heat may be eliminated in the manner shown in they modified form, Fig. 4.

In the form shown in Fig. 4, the bulb and socket arrangement have been broken away and the stem is shown as holding the internal parts of the device, but it is understood that this form is also to be incorporated in such a bulb and socket arrangement as shown in Fig. 2/ In Fig. 4, a bifurcated bi-metallic actuating strip 26 has spaced downwardly extending legs fixed, such as by welding, to respective anchors 2! and 28. Another anchor 29 carries 'a movable contact strip 30 fixed thereto and an anchor 3| carries a bi-metallic strip 32 which is oppositely arranged to the bifurcated bi-metallic actuating strip 26, or that is, these bi-metallic strips 26 and 32 are arranged so that temperature changes tend to produce deformation thereof in opposite directions, or in this case an increase in temperature tendsto actuate the strips toward each other.

An'insulating member 33 rigidly connects the extreme upper ends of both bi-metallic strips 26 and 32 to the movable contact strip 30, which insulating member 33 has two openings spaced each side of this 'movable contact strip 30. Two

contact members 34 and 35 are fixed to respective anchors 36 and 3! at each side of the strip 30 so as to extend through the aforesaid openings in the insulating member 33 with thecontact member 34 normally engaging a low resistance contact point 38 on the strip 30. The anchors 21, 2B, 29, 36, and 31 have the lead-out wires 23 connected to the lower ends thereof which extend through the glass stem 5 for connecting to terminals such as the prongs 24 shown in Fig. 2.

It is evident now that when a difference in potential is applied to the anchors 21 and 28 through their leads 23, current will flow through one leg of the bifurcated actuating strip 26 to the upper end and back through the other leg, and if this current is of a substantial value, sufficient heat will be produced thereby to effect deformation of the strip 26 to the right which will operate the contact strip 30 through the member 33 to a position engaging the contact member 35. As previously stated, the current required to effect actuation of this strip 26 is comparatively small because the dissipation of the heat produced is greatly retarded by the vacuum or reduced gaseous pressure surrounding the relay elements. The bi-metallic strip 32 being oppositely arranged to the actuating strip 26 is effective to maintain a definite relation between the movable contact strip and the fixed con tacts 34 and for ambient temperatures and consequently should be of a predetermined cross section which will produce equal deformation when at all temperatures which are equal to the temperatures of the actuating strip 26.

The present invention may be used in any circuit in which a time delay is required between energization of the relay and the closing or opening of a controlled circuit, or for example, it may be applied in the railway signalling art in the manner disclosed in prior application of R. M. Phinney, Ser. 'No. 463,940 filed June 26, 1930. It is also obvious that the modified form of the present invention shown in Fig. 4 may be further modified by constructing the -bi-metallic strip 32 the same as strip 26 and by providing a means for conducting current therethrough this form may be power operated both toward the front contact 35 as well as back toward contact 34 to its normal position A means for accomplishing this result and a circuit employing such power driven over-and-back operation is fully shown and described in the prior application of Joseph E. Willing, Ser. No. 551,931, filed July 20, 1931.

A relay has thus been provided having a thermal operated element enclosed within an evacuated tube thereby permitting a filament of iron or other material having current regulating characteristics to be used which may be heated to substantially any temperature without oxidation thereof. The characteristics of the filament are such that current drawn during operation of the relay is substantially constant regardless of variations in the energizing voltage in as much as the resistance of the filament increases rapidly and out of proportion to the current increase as the temperature thereof tends to increase. The evacuation or reduced inert gaseous content of the tube also greatly increases the current carrylng capacity of the contacts by preventing oxidation of the contact metal when either making or breaking circuits carrying a substantial amount of current.

Because of the fact that the present relay may be adjusted to have a very small operating movement and because the evacuation or reduced gaseous pressure of the inclosure greatly retards heat radiation, avery small amount of heating energy is required for the relay operation. The effectiveness of the energy used by the filament in the first described form is increased by the reflectors which are arranged to concentrate the heat produced by this energy directly upon the thermal responsive operating strip thus further adding to the efliciency of the device. The second described form is obviouslyvery emcient in as much as the heat is generated directly in the operating strip and is dissipated very slowly because of the surrounding vacuum. Another very important feature of the present invention is the increased accuracy of the ambient temperature regulation, or the automatic regulation of the operating time regardless of the surrounding atmospheric temperature, and this is .obtained both by the increased efiectiveness of the compensating means due to the smaller operating movement and also because the vacuum or reduced gaseous pressure surrounding the thermal responsive elements of the device eliminates to a great extent the effect of the atmospheric temperature thereon.

The filling of the bulb enclosing the relay with an inert gas, or the evacuation thereof has been stated as optional because the election of either method will depend largely upon the operating time requirements of the particular application. If the inert gas is used, the advantage of preventing oxidation of the filament and contacts is retained, but the operating characteristics are changed by the increased facilities for transmitting heat within the bulb due to the presence of the gas. For example, the heat from the filament is transmitted only by radiation in an evacuated bulb while the transmission is aided by conduction and convection when the bulb is gas filled thereby reducing the time required for the relay actuating element to return from its heated position to the normal position in such a gas filled enclosure. It is also probable that the time required for the normal operation or operation eifected by heating the filament may be increased in the gas filled bulb due to the increased tendency forthe heat to be conducted from the filament to the bi-metallic contact strips thereby requiring a longer time to obtain the difference in temperature between these contact strips and the center actuating strip which is required for operation. From the above, it will be evident that the degree of the change caused by substituting a gas for the vacuum in the bulb will be substantially proportioned to the amount or pressure of the gaseous content of the bulb.

The above rather specific description of one form of the present invention is given solely by the way of example, and is not intended, in any manner whatsoever, in a limiting sense. It is also to be understood that various modifications, adaptations and alterations may be applied to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention, except as limited by the appended claims.

Having thus described my invention, what I claim is:-

1. In a thermal relay, an evacuated bulb, a glass supporting stem within said bulb, spaced anchors moulded in said stem so as to extend within said bulb, a bi-metallic actuating strip attached to one of the anchors, a current regulating filament associated with said actuating strip, reflectors arranged to concentrate heat from said filament upon said actuating strip, and bi-metallic contact strips attached to other of said anchors and positioned to be selectively engaged by said actuating strip, said contact strips being arranged so that temperature changes produce equal deformation and in the same direction as produced in said actuating strip.

2. In a thermal relay, an evacuated bulb, a

glass supporting stem within said bulb, spaced anchors moulded in said stem so as to extend within said bulb, a bi-metallic actuating strip attached to one of the anchors, a current regulating filament associated with said actuating strip, reflectors arranged to concentrate heat from said filament upon said actuating strip, bi-metallic contact strips attached to other of said anchors and positioned to be selectively engaged by said actuating strip, and supporting means for said filament attached to anchors holding said reflectors whereby electrical energy may be conducted to said filament.

3. In a thermal relay, an evacuated bulb, a glass supporting means in the bulb, front and back contact means within said bulb, a thermal element held by said glass supporting means and positioned to move between said front and back contact means, bimetallic contact supports arranged to maintain said front and back contact .means in a definite relation to said thermal element when at equal temperature therewith, and an iron wire heating filament associated with said thermal element.

4. In a thermal relay, an evacuated bulb, a glass supporting means in the bulb, front and back contact means within said bulb, a thermal element held by said glass supporting means and positioned to move between said front and back contact means, bi-metallic contact supports arranged to maintain said front and back contact means in a definite relation to said thermal element when at equal temperature therewith, a current regulating heating filament, and means at each side of said thermal element arranged to shield said contact supports from said heating filament. V

5. In a thermal relay, an evacuated bulb, a glass supporting means in the bulb, front and back contact means within said bulb, a thermal element held by said glass supporting means and positioned to move between said front and back @ontact means, bi-metallic contact supports.arranged to maintain said front and back contact means in a definite relation to said thermal element when at equal temperature therewith, a

current regulating heating filament, means at 7. In a thermal relay, a bi-metallic actuating strip, a current regulating filament associated with said actuating strip, reflectors arranged to concentrate heat from said filament upon said actuating strip, and bi-metallic contact strips positioned to be selectively engaged by said actuating strip, said contact strips being arranged so that temperature changes produce equal deformation and in the same direction as produced in said actuating strip.

8. In a thermal relay, an evacuated bulb, a bimetallic actuating strip in the bulb, a current regulating filament associated with said actuating strip, reflectors arranged to concentrate heat from said filament upon said actuating strip, bi-

metallic contact strips positioned to be selectively engaged by said actuating strip, and supporting means for said filament.

9. In a thermal relay, an evacuated bulb, front and back contact means within said bulb, a thermal element positioned to move between said .front and back contact means, bi-metallic contherewith, and an iron .wire heating filament.

associated with said thermal element.

0. S. FIELD. 

